Artifactual complement activation by blood-drawing apparatus. A clinical and investigational caveat

An increase in the occurrence of false-positive assays for C5a and C3 conversion, combined with hemolytic C assays discrepant between two laboratories, led to the suspicion that serum tubes with silicone separators might activate complement. Plasma incubated with some lots of such tubes showed evidence of complement activation via the alternative pathway, to an extent capable of influencing interpretation of results. The authors recommmend that such tubes not be used for C split-product assays, and be used only with caution for routine hemolytic C assays.